Cognitive Dissonance In Action: Glucosamine No Matter What!

I’ve discussed cognitive dissonance previously. Briefly, it is the unpleasant feeling that comes from a conflict between beliefs, and its most typical manifestation is a powerful ability to rationalize away evidence that contradicts what we believe. Rather than experience the discomfort of recognizing and accepting that our beliefs are mistaken, and that as a consequence we may have acted inappropriately, we simply find ways to dismiss even powerful evidence and cling to our false beliefs.

I recently came across a classic example on the blog of a “holistic” veterinarian. The evidence, which I’ve reviewed before (HERE, and HERE, for example) is quite clear that in humans oral glucosamine and chondroitin are no better than a placebo for arthritis. And the limited evidence available in veterinary medicine provides no better support for these supplements. As the evidence against these products accumulate, the rational thing to do is to re-evaluate our use of them and honestly advise our clients that the best we can say is they are harmless and may have minimal benefit for selected individuals. This, however, is problematic for those with strong ideological commitment to supplements being superior in terms of safety and efficacy to conventional medicines.

The vet in question acknowledges that recent research suggests a lack of effectiveness for these products, but his response has more to do with his biases than a rational analysis of the risks and benefits of various therapies.

If consumers believe some of the recently published articles that purport to show a lack of effectiveness for joint supplements, my concern is that they will turn to chronic NSAID usage which could be harmful or even fatal due to the well-known side effects (kidney disease, liver disease, worsening of the arthritis, gastrointestinal ulcers and perforations) of this class of medications.

So, if consumers realize glusosamine isn’t doing anything for their pets, they might be tempted to switch to drugs that actually do help? Isn’t that awful!

There is no question NSAIDs have potential side effects. Any medication that has benefits does. The issue is whether we are better off giving our pets an absolutely safe product that does nothing, or a very safe product that really helps. Research clearly shows NSAIDs have undeniable benefits for arthritis patients, far greater than any potential benefits of glucosamine products.[1,2] And the safety record is very good, with serious side effects in only a small percentage of cases, even with long-term use, and with most problems associated with inappropriate use (dose higher than recommended or used at the same time with steroids or other NSAIDs)[3-5] These drugs can worsen pre-existing kidney or liver disease, but this is preventable with appropriate screening and monitoring. The can cause gastrointestinal ulceration in a small percentage of patients, though this is rarely clinically significant. They do not worsen arthritis. And, as the good holistic vet neglects to mention, these medicines actually do treat arthritis effectively, unlike glucosamine.

The mental contortions involved in continuing to recommend an ineffective product can be quite complicated. In addition to ignoring the benefits of NSAIDs and the lack of benefits to glucosamine and focusing only on risks, the denial of reality involves ignoring research findings if one can find anecdotes or personal beliefs that contradict them.

Additionally, many consumers currently using joint supplements experience the positive effects commonly seen with these products, including relief from pain, reduced inflammation, reduce joint swelling, and increased mobility. While skeptics may claim it is only a placebo effect (and in some case they may be correct,) if the end result is an improved quality of life, does it really matter why the patient feels better or gets better?

This response not only inappropriately privileges anecdote over research evidences, it also reflects a common misunderstanding of the placebo effect. It is not a case of “mind over matter” in which the patient gets better because they believe they are being treated. It is a case of patients believing they are better and reporting a positive effect when their disease has not actually changed. One can argue this may be of some real benefit for people with subjective symptoms, like pain and nausea, since thinking you feel better might in some sense actually be feeling better. But the effects are always small (far less than those of  truly effective medicines), they don’t last, they don’t change the underlying disease process, and they require the healthcare provider to either be wrong about whether the treatment actually works or to lie about it. Is this really better than using medicines that have high benefits and some risks?

This vet then exaggerates his own personal experiences and ignores the many ways in which veterinarians and owners can be mistaken about the effects of a treatment, to present what looks like a incontrovertible case against the research findings.

In my own veterinary practice, the placebo effect cannot occur. Either my canine and feline patients improve and begin walking, or they don’t and they remain lame. I have seen thousands of pets improve when administered joint supplements and taken off of NSAID medications. Neither the owners or I were making this up. Either the pet walks or it doesn’t walk: this is not a placebo effect.

This makes it sound like this fellow has seen thousands of pets who couldn’t get up take glucosamine and then rise and walk. If these products really are such a miracle drug, why isn’t this obvious to everybody else taking or prescribing them? I suspect the truth is that he recommends glucosamine for dogs with signs of arthritis, and later the owners say “Gee, I think Fluffy’s walking better!” This may be true, but it’s also quite likely may be a result of the  “placebo by proxy effect.” This is a combination of many of the cognitive errors I’ve written about before: Regression to the mean/natural course of disease (in which a patient with a waxing and waning problem comes in right when the symptoms are at their worst and are just about to get better as part of the natural course of the condition); expectancy (in which the owner expects to see some improvement as a result of the time, effort, and money they’ve spent on seeing the vet and so convinces themselves they have); and all the inadequacies of subjective, external evaluation of an animal’s level of pain that make real, objective research in this area so vital.

Finally, this alternative vet comes right out and says that he doesn’t believe the research, because it contradicts his personal experiences, and that he has no intention of re-evaluating his beliefs regardless of what evidence comes to light.

While I appreciate ongoing research into the use of joint supplements, I still encourage people to use joint supplements for themselves and to administer them to their pets. I have seen the effectiveness of these products and have also seen the horrible side effects of chronic NSAID usage. While researchers can continue to fight over the effectiveness of joint supplements, I will continue to use them and other treatments that help improve the lives of my patients.

This is the paradigm of cognitive dissonance and faith-based medicine. The same reasoning supported millennia of bloodletting and all manner of useless, even harmful therapies that modern medicine has only been able to dislodge by demonstrating that we must have the humility to accept our personal observations are less reliable than true scientific evidence, and the courage to acknowledge when we have been mistaken and change our ways. No such humility or courage is possible with a deep ideological commitment to alternative ways and an irrational suspicion of all things based in mainstream science. For all that advocates of such an approach call for “open-mindedness” regarding their own ideas, they don’t very often evince it when it comes to the evidence against their favorite therapies.


1. Aragon, C.L., Hofmeister, E.H., Budsberg, S.C., Systematic review of clinical trials of treatments for osteoarthritis in dogs. J Am Vet Med Assoc 2007; Feb 15;230(4):514-21.

2. Moreau, M., et al. Clinical evaluation of a nutraceutical, carprofen, and meloxicam for the treatment of dogs with osteoarthritis. Vet Rec 2003; 152:323-329

3. Innes JF, Clayton J, Lascelles BD. Review of the safety and efficacy of long-term NSAID use in the treatment of canine osteoarthritis. Vet Rec. 2010 Feb 20;166(8):226-30.

4. Lascelles BDX, Blikslager AT, Fox SM, Reece D. Gastrointestinal tract perforation in dogs treated with a selective cyclooxygenase-2 inhibitor:29 cases (2002–2003). J Amer Vet Med Assoc 2005; 227(7):1112-7.

5. Neiger R. NSAID-induced gastrointestinal adverse effects in dogs—can we avoid them? J Vet Intern Med 2003;17:259–261.

This entry was posted in General, Herbs and Supplements. Bookmark the permalink.

9 Responses to Cognitive Dissonance In Action: Glucosamine No Matter What!

  1. v.t. says:

    I’m surprised he didn’t go into his usual spiel that homeopathy and supplements cure everything those evil conventional vets can’t.

    Seems he gets some weird pleasure in stalking your blog so he can write rebuttals on his own blog. No creativity, there. But quite amusing 🙂

  2. Alison says:

    About the harmlessness of glucosamine for animals: there is some evidence that it can worsen insulin resistance in people (sorry, can’t find link but it’s referenced in Wikipedia). Could this be the case in other animals too? I’m thinking here of horses who are given glucosamine because they have arthritis, but their arthritis is linked to their being overweight, and their overweight is linked to their being insulin resistant. And if the supplement makes the insulin resistance worse … A vicious circle one would possibly wish to avoid

  3. skeptvet says:

    The data I’ve found on insulin resistance in humans are conflicting and of questionable clinical relevance:

    The limited data in veterinary patients doesn’t suggest a real clinical danger, but of course it is limited in quantity and quality:

  4. Pingback: Glucosamine – going the way of echinacea (and with just as many hanging on to their belief – in spite of all evidence) « Gilgablog

  5. Rita says:

    Golly, Alison, that’s pretty alarming – is this an extra risk for elderly, Cushings horses?

  6. Alison says:

    That was my thought, Rita, and I had wondered whether there might be a connection between the well-documented increase in Cushings and other metabolic disorders in the UK over the last few years, and the concomitant rise in giving glucosamine to attempt to prevent as well as treat arthritis, but if as Skeptvet says there is unlikely to be a clinical effect I am probably mistaken.

  7. Tony says:

    I am so happy to have found your blog. I have long considered myself a rationalist and skeptic and just someone who is deeply distrustful of the (many) unsupported claims of the holistic medicine crowd. But it is soooo hard not to give in when you see your beloved pet struggling. My eleven year old German shepherd has arthritis in a hind knee resulting from an ACL injury six years ago (followed by TPLO surgery). For the most part he seems to be coping pretty well, but he does have days when he is very stiff. Recently, despite my internal quackometer going off loudly, I found myself buying glucosamine and condroitin supplements at the urging of just about everyone at the dog park. Mind you, most of the local proponents of glucosamine are also giving their dogs NSAIDs such as Metacam and so I don’t know how they would be able to tell which treatment is working. The thing that I find most interesting is that there is never any differentiating between the two by the dog owners I come across — they treat both as though they are scientifically proven treatments. I think I’ll have to start subtly mentioning around the dog park.

  8. skeptvet says:

    Glad you found it useful!

    There are lots of perfectly legitimate reasons people reach for unproven treatments, or even those that are clearly ineffective, and I certainly wouldn’t blame anybody for wanting to do everything they can for their pets. I only hope that having access to all the information will help people make better decisions and avoid things that don’t really help.

  9. Pingback: What Is The Best Glucosamine For Dogs – And Does It Really Work – The Labrador dogs

Leave a Reply

Your email address will not be published. Required fields are marked *